Higher order pressure gradient microphone system having adjustable polar response pattern



July 21, 1959 Filed Feb. 8, 1952 WIGGINS HIGHER ORDER PRESSURE GRADIENT MICROPHONE SYSTEM HAVING ADJUSTABLE POLAR RESPONSE PATTERN 4 Sheets-Sheet 1 {DSH/FTER 2/! J7 AT/ENUATOR MIXER E "B j? PSH/FTER 1 A7IENUA r013 MIXER A jj a5 F ER 57 P flfrzzuzm 26 )8 i D a )3 0 SH/FTER AUEMUATOR MIXER ,23 A#ZSLZR L co/vmo (5 j?! {riff 1 j7! (L -MIXER P T AMP ATTENl/A TOR I (B 121 1.55 131 MIXER w sH/Fr R M/XEr? AMP AT/ENUATOR it .3 155 MIXER SH/FI'TER #MXER f D AMP ATIENUA TOR a f2 127 J33 MIXER flSH/FTER AMP A772 UA TOR MIXER CONTROL 6-129 I #5 17 i 17 X E R s sfl/rrsg'? MIXER --M/XER M I x ER Armvunro R I I G 176 179, 184 F M O-* MIXER flay/F75? 1 O MIXER UZ-WUATOR MIXER v XER A 166 161? 5 159 r X SHIIIPTER B MIXER i M/XER- K i O-- M /X ER i j65 [156; 187 X ER flab/PIER M IXER AT/E/VUA TOR MIXER M I X [R I CONTROL Y R' jgo 940/262 M was BY Ju y 1 A. M. WIGGINS 2,896,189

HIGHER ORDER PRESSURE GRADIENT MICROPHONE SYSTEM HAVING ADJUSTABLE POLAR RESPONSE PATTERN Filed Feb. 8, 1952 4 Sheets-Sheet 2 INVENTOR. I

July 21, 1959 Filed Feb. 8, 1952 A" M. WIGG NS I HIGHER ORDER PRESSURE GRADIENT MICROPHONE SYSTEM HAVING ADJUSTABLE POLAR RESPONSE PATTERN 4 Sheets-Sheet 3 lid 21a 17! 1 2 9 at? 217 K 216' l 1 70 l IOTHER 5 M3 2 M/xER$ 2 A .9 12-: 190L .---i

w INVENTOR. a! lea M z' 5725' BY 17 Y July 21, 1959 v A. M. WIGGINS 2,896 189 HIGHER ORDER PRESSURE GRADIENT MICROPHONE SYSTEM H VING ADJUSTABLE POLAR REI PONSE' PATTERN v A Filed Feb. 8, 1952 v 4 Sheets-Sheet 4 United States Patent ice Alpha'M. Wiggins,- Buchanan, Mich., assignor to Electro- Voice lncorporated, Buchanan, Mich.

, Application February 8, 1952,-Serial No. 270,564

sClilims. ((31.340-6) I The present invention relates to a higher order pressure gradient microphone system wherein the polar response pattern may be oriented as desired; eithercontinuously orto a particular direction.

It'frequently is desired to provide a microphone system fordetermining with accuracy the direction of a source of sound with respect to a point or to obtain an indication ofi'the movement of a sound source. Heretofore, this generally has beenaccomplished by a'relatively large heavy apparatus which isymechanically loaded forscan ning. Such apparatus is' rather expensive and requires a control mechanism which will produce movement of the apparatus at a steady rate without introducingundesired responses or noise into the microphone'system.

It, therefore, would be desirable to provide a. micro phone system having a highly directional polar pattern which could be shifted or rotatedas desired by theme of electrical lcircuit means thereby, obviating the necessity for elaborate mechanical apparatus. In accordance with the present invention, it is proposed to arrange microphones in' a pattern and to'utilize electrical circuit means to diiferentially combine selected components from thefiseveral microphones to produce a highly'directional polar pattern of desired orientation. 7

It, therefore; is an object of thepresent invention to providea highly directional polar pattern in a higher order pressure gradient microphone system.

7 Another object of the present invention is to' provide ahigher order pressure gradient microphone systemwherein'the polar response pattern maybe shifted asdesired.

' A further: object of the invention is to provide a'higher order pressure gradient'microphone system arranged to utiliZe a directional polar pattern for scanning without mechanically moving the microphones, I

" Still another object of the invention'isito providea higher order pressure gradient microphone system to Figure 4 is a circuit diagram illustrating of the system shown in Figure 3; j I V I Figure 5 is another circuit diagram for obtaining af still higher orderpressure gradient microphone 'systemtf Figure 6 is a' circuit diagram illustrating certain details of the systemshown in Figure 5; and K Figures 7; 8, 9 andlOare polar'diagr-ams to aid in ex"- plaining the operation of the present invention; v Referring toFigure l of the drawings there'is shown in the-circuit diagram aplurality of microphonesA; 'B;

eertain' detat1 C, D and'E'arranged in a pattern. Preferably fortlie convenience" of constructing the system and explaining the operationthereof these microphones are arranged'at' points in asymmetrical or geometrical figure. Thusfthe microphonesB, C, D and E appear at thecorners of: a

. square whereas the microphone A is located at the inter section: of the diagonals of; the square; These micro phones are arrangedat'a distance from each other bearing a selected relation to the wave lengths of the'principal' frequencies towhichth'ey are expected to respond. It will be appreciated thatfor certain purposes the construe tion and .operation of' the system contemplated can be simplified by selecting a'frequency'response band covering theprincipal soundswhich are to be detected. Each of the microphones A, B,.C,.D and E: is connecte'd to' its respective amplifier 11; '12, 13,14 and'1'5,' the output of Which'is connected to the respective phase shifter'and'attenuator 16517; 18, 19 and; Each'of the phase shifters and attenuators 16 to 20 is provided with one or: more variable or adjustable circuit elements arranged'to beoperated in'accordance with a common' control mechanism 21. The control mechanism is not necessarily a unit control of all of these devices,. but maybe a servo system'or sequence operation system so that at various times'in a cycle of operation different amounts of phase shift and different'degreesof attenua tion" are produced so that output voltage components of desired magnitude may be obtained. 7 p g Two of the phase shifters 11 and 21 are connected to a mixer122'. Similarly two other phase shifters and attenuators118' and 19 are connected to a mixer 23.

Thus, it will be seen that the four corner microphones determine with accuracy the direction of a source 'ofsound scription taken in conjunction with the accompanying drawings wherein: I V t Figure 1 is a block diagram of one higher order pressure gradient microphone systemfor obtaining an ad justable polar response pattern; I

Figure 2, is a circuit diagram illustrating certaindetails of'the systemof Figure 1; f i I Figure 3 is another circuit diagramqfor-a systemrfor obtaining results similar to that obtained by-jthe system shown in Figure 1; a

B, C, D and E supplyjenergy tothe mixers 22"and 23: The outputs of the mixers 22 and 23'ar'e combined'in a mixer '24 whichuisjconne cted to one of the output ter minals 25; the other output terminal being connected to the ground; Thephase shifter and atten'uator 1-6 serving the microphone A has its output connected'to the output tenninall5i, A v I a Before. endeavoring. to oiferfurther explanation of the purpose and operation of the block diagram system shown i-n Figuregl, reference may be hadtoFigur-e 2 which-illustrates certain circuit details. In Figure 2, therejis shown the amplifier 11 which may, be a triod yaeuu'mtube 27'hav'ing-its grid'pjrovidedwitha grounded resistor 28'. The grid is also connectedfto a microphone jack] A. The lc'athodeiofjthe vacuum tube.27, isprovided with a grounded biasresistor 29 shunted. by' a by;- pass capacitorjSl; Suitable anode potentialfis supplied to the-vacuum tube 27vth'rough an anode couplingre; sistori 32. The anode ofithe vacuumtubef27 'is connected through a' coupling pcapacitor 33 to-one end of a voltage divider resistor or potentiometer34 having its other" terminalconnected to the common junction betweenitwo cathode'resisto'rs 35' and. 36 of. a vacuum tube 37- The. grid of the vacuum tube v37 'is connected :to an adjustable contact 38 of the voltage divider resistor 34. Thevacuunr tube. 37 and its-associated circuits is-a-part of thephase shifter and attenuator 16 shownin Figure'l; and the vacuum tube, 11 and its associated circuits constitute the amplifier '11 of Figure 1.: :S uitable anoderpotentiak is Patented J 1:95?

s upplied to the vacuum tube 37 through an anode coupling resistor 39.

The anode of the vacuum tube 37 is connected to a coupling capacitor .41 which is. connected to. an adjustable co'ntaict 42 of a resistor 43 having one end connected to the cathode ofthe vacuunitube'37. The adjustable contactj42 is connected to a coupling capacitor .44 connected to the grid of avacuum tube 45. The grid of the vacuum fube 45 is providedwith a grid resistor 46 having one end connected between the common junctionoftwo cathode resistors 47 and 48. Suitable anode potential is supplied to the anodeof vacuum tube 45 through an anode coupling resistor 49. The anode of the vacuum tube 45 is connected to a coupling capacitor 51 which is connectedto the adjustable contacts 52 of a resistor 53 having one end connected directly to the cathode of the vacuum tube'45. The adjustablecontact 52 is connected to a coupling capacitor 54 which is connected to the grid of vacu um tube 55. The vacuum tube 55 is provided with .af'grid resistor 56connected to ground. The cathode of the vacuum tube 55 has a cathode biassing resistor 57 connected to ground which is by-passed by a capacitor 58. Suitable anode potential is provided for the vacuum tubeISS .jthrough an anode coupling resistor 59. The anode of the vacuum tube 55 is connected through a loading resistor 61 and acoupling capacitor 62 to the output terminal 25. l Z

.A microphone jack C is connected to the grid of a vacuum tube 63 having a grid resistor 64 connected to ground. .The cathode is biassed by a cathode resistor 65 which is by-passed by a capacitor .66. Anode potential is supplied to the vacuum tube 63 through an anode coupling resistor 67. The vacuum tube 63 and its associated circuits constitute the amplifier 13 shown in Figure 1. p

The anode of the vacuum tube 63 is connected to a coupling capacitor. 68 connected to one end of a voltage divider resistor 69 having its other end connected to the common'junction between the cathode resistors 71 and Hot a vacuum tube 73. The adjustable contact 74 of the resistor 69 is connected to the grid of the vacuum tube 73. Anode potential from a suitable source is supplied through an anode coupling resistor 75. The'anode of the vacuum tube 73 is connected to a coupling capacifor 76 which is connected to an adjustable contact 77 of afresistor. 78 having one terminal connected directly to the "cathode of the vacuum tube 73. The adjustable contact-77 of the resistor 78 is connected through a coupling i :apacitor,79 to the grid of a vacuum tube 81. The grid ofthe vacuum tube 81 is provided with a grid resistor 82having one end connected to the common junction between cathode resistors 83 and 84 of the vacuum tube 81:"The anode is connected through a c'oupling'capacitor 86 to an adjustable contact 87 of a resistor 88 having one end connected directly to thecathode of the vacuum tube s1. I ".The jadjustable contact 87 of a resistor 88 is con nected through a coupling capacitor 89 to the grid of a vacuum tube 91. The grid of the vacuum tube 91 is pro vided with a grid resistor 92 connected to ground. The cathode of the vacuum tube '91 is provided with a cathdde bias resistor 93 which is by-passed by a capacitor 94. Suitable anode potential is supplied through an an-r odecoupling resistor 95 to the (vacuum tube 91. j p 1" The anode of the vacuum tube 91 is connected through a loading resistor 96 to a coupling capacitor 97 which is connected to the grid of a mixer tube 98. The grid of themixer tube is provided with a grid resistor 99. The coupling capacitor 97 is connected to another loading re: sistor 101 which is connected to" the phase shifter and attenuator 19 of the microphonejD of Figure 1. It will be' noted that the vacuum tubes 73, 81 and 91 together with their associatedcircuits'constitute the phase shifter arid attenuatorl8 of Figure 1-. The cathode of the vacuum tube 98 is provided with a'bias resistor 102 which is by-passed by a capacitor 103.

Anode potential is supplied to the vacuum tube 98 through an anode coupling resistor 104. The anode of the vacuum tube 23 is connected through a loading resistor 105 to a coupling leapacitor 196 which is connected to the grid of a vacuum tube 107. The grid of the vacuum tube is provided with a grid resistor 108. The cathode of the vacuum tube 107 is provided with a grounded bias resistor 109 which isbypassed by a capacitor 111. Anode potential is supplied to the vacuum tube 107 through an anode coupling resistor 112. The anode of the vacuum tube 107 is connected through a loading resistor 113 to the juncture between the coupling capacitor 62 and the loading resistor 61. The grid of the vacuum tube 106 is connected through the capacitor 107 to a loading resistor 114 which in turn is connected to the mixer 22 of Figure 1. The vacuum tube 107 and its associated circuits constitutes the mixer 24 of Figure 1.

. Since, however, the microphones B, C, D and E each have a circuit associated therewith similarto the circuit appearing in Figure 2 between the microphone jack C and the coupling capacitor 97 of the circuit of the mixer tube 98,. it is not deemed necessary to show all the remaining circuits. The phase shifter and attenuator for the microphone C hasadjustable contacts 74, 77 and 87 operating on their.associated resistors and connected to be. controlledby the control mechanism 21. Similarly the phase shifter 16 of the microphone A has adjustable contacts 38, 49 and 52 which likewise are controlled by the control mechanism or system 21.

It is well known that a pressure gradient microphone system may be construction from two adjacent pressure microphones by placing them in tandem with their signal generating systems connected in opposition. This results in a first order pressure gradient microphone arrangement having polar response pattern generally corresponding to that shown in Figure 7. i Asecond order gradient microphone system can be obtained by using pressure microphones A, B and D of Figure 1. The output voltages of the microphones Band D are connected in, series. Twice the output voltage of the microphone A is subtracted from this combined output. The resultant polar response characteristic will i be similar to that shown in Figure 8 which curve is cos2 6. It will be noted that the response characteristic has a maximum response in two directions from the point A. The response characteristic can be changed to a unidirectional one by introducing a phase shaft in the outputs of the microphones B and D. An electrical phase shifting network whosephase shift is proportional to frequencyis connected to the output of the microphone D to produce a lead in phase equal to the lead in phase produced from sound travelling from the position of the microphone D to the microphone B. A similar phase shiftingflcircuitis connected to the microphone B to producea'lag in phase equal to the lag in phase produced by sound travelling the distance between the microphones A and .Ba The resultant polar response characteristic is represented by a polar curveshown in Figure 9 which is (H-cos 0) cos 0. t 1

' .From the foregoing. it becomes apparent that another unidirectional response can be obtained from the microphones EAC at right angles to that obtained from the microphones BAD. This is shownby the dotted line representation in. Figure 9. By. suitable control of the amplitude of thevoltagecomponents derived from each microphone output and the phase shifting circuit with respect to the microphones B, C, D and E a similar polar response curve can be obtained, as illustrated by Figure 9,- which will have, its maximum pick up. at any selected angle as determinedb'y the amount of phase shift introduced by the various circuits and the magnitudes of the voltage components derived from the outputs er the several; microphones.

- When microphones B and D are connecteddi fierentially and microphones D and A are also connected dif- When this phase shift is equal tothe phase shift pro duced by sound travelling between the microphone combinations BD and DA, factorsa. and-bbecome equal to one. From this combination a polar pattern (1+cos 0) cos 0 as shownin'Figure 9 results. The difference between this condition and a partialphase shift is illustrated by the representation of the response characteristic in Figure '10. 1t will'be noted that this is a unidirectional response which gives a result comparable to that shown in Figure 9. This, therefore, indicates 'thata certain latitude in the control of the several phase shift circuits shown in Figure 1 is possible and yeta unidirectional polar response characteristic can be obtained which may be shifted through 360.

Reference may now be had to Figure 3 which shows another block diagram of an arrangement for. obtaining response characteristics similartothat obtained by the system shown .in Figure 1. For convenience in comparing this arrangement with that shown in Figure l, five microphones again have been utilized at "the locations A, B, C, D and E. The microphones'B,C, D and E are connected respectively to mixer amplifiers 121, 122,

123 and 124. The microphone A is connected to each of these four mixer amplifiers. ,Each of these mixer amplifiers 121 through 124 is connected to one of the phase shifters 125, 126, 127 and 128 which are subject to a control 129. These phase shifters and attenuators 125 to 128 are connected through mixers 131 through 134 to the output terminal 135, the other output terminal 136 being 'connected to ground.

'Since the circuit arrangement for each of the microphones B, C, D and E is the same it will be necessary only toillustrate the circuit arrangement for one of these microphones as shown in Figure '4. From this it'wi'll be seen that the mixer amplifier 121 has two tubes 137 and 138 having their anodes connected together andhaving a common anode coupling resistor 139 which in turn is connected to a' suitable source of anode potential. The cathodeof the vacuum tube '137 is connected to a bias resistor 141 which in turn is connectedto ground. The grid-of the-vacuum tube 137 is connected" to a grid resistor 142 which also is connected toground. The-grid of the :vacuumtube 137 is connected tothe microphone jack B.

.The .vacuum' tube 138 has its grid connected to the microphone jack A and to a grid resistor 143 which is connected to' ground. 7 The cathode of I the vacuum tube .138 isconnectedto a bias resistor '144 which is also connected to: ground. The anodes of the vacuumtubes -137 and 13.3 are connected to a couplingcapacitor 145 which is connected to one terminal of a resistor 146 having its" other terminal connected to the juncture between cathodebiassing resistors '147 and 148 .of a vac- -uum:tube:.149. One end of the cathode resistor 148 is connectedito ground. The grid of the vacuum-tube 149 iSfCOl'lIlCifidiO an adjustable'contactlSl of a resistor 1146. Suitable. anode potential-is supplied to the vac .uum tube.149.through the anode coupling resistor 152. The ianodeof the vacuum tube149'is connected to a Anode potential. is supplied to :the vacuum tube.157..from the. anode source throughacoupling resistor, 162. The anodev is connected-through a coupling capacitor 163 to the adjustable contact 164 of-a resistor .165 having one end connected directly to the cathode of the vacuum. tube 157. The vacuum tubes 149 and 157' "constitute-the phase shifter and attenuator .125 of Figure .3.

. The. adjustable contact 164. of {the resistor nected througha couplingcapacitor 166 tothef grid .of a vacuum tube 167. The grid is. also connected to agrid resistor 168 having ..one-.end connected .to ground. .A cathode biassing resistor 169 is connectedbetween ground and the vacuum tube 167. The anode of thevacuum tube 167,is connected to .the anodes of-three. similar tubes of mixers 132,133 and 134. ,The vacuum tuhe 167 and its associated circuits constitutes the mixer ,131

- of Figure 3. All of these, mixerslhavea commonanode coupling resistor 17.1 and they are connected to, acoupling capacitor 172 whichvis connected to one of the output terminals 135. vTheadiustable contacts 151, 154 and 164 of the resistors14'6, 155 and 165 are Operated by the'control 129. This controldeterminesthe amount of phase shift and attenuation in order to prod'uce the polar response characteristic at a desired orientation. i

From the foregoing .it.will become. apparentth'atrin Figure 3 the outputs of mixers B, C, D and E are each mixed difierentially vwith the output of microphone A to produce ajbi-directional pressure gradient response such as' that shown in Figure 8. After. passing through thephase shifters and attenuators these combined volt: agesareagain mixed diflerentially'to producea directional characteristic comparable to those illustrated in Figures 9;and 10. The general form of the resultant polar response characteristic is (a l-b cos 0) cos 0 where 0-is theanglen1easured from .the angle of maximum pick-up. V

Thus,'it will be appreciated that by meansrof electric controland without any mechanical movement other than the adjustableresistor, contacts shown inpFigures 2 and 4 an'action'can'be obtained similar to thatpreviously produced byrnechanical systems ,which rotated twojspaced apart microphones. In addition, the present invention contemplates successive differential combinations of'the outputs of the microphones to provide still higherorders of directional response. Thus, higher orders of pressure gradient microphone systemscan be obtained than as was possible byqthe mechanical systems, An example of a still higher ordersystem. of pressure gradient response is shown in the blockidiagram of Figure 5. In this arrangement, a larger number of microphones is employed which for sake of illustration coupling capacitor 153 which is connected to an adjustable contact 154 of-aresistorg155 which has one end connected-directly to the cathode of the vacuum tube 149.

'1The-adjustablecontact,154 of the resistor 155. is convnected through a coupling capacitor 156 to the'grid .of

are arranged along the'diagonals of a square "or along two-lines perpendicular-to. each other. Four micro: phones F, G, and K are arranged at theeornersjf a large square{ Four other microphonesLjM, N and O are arranged at'the corners ofa .smallensquare symmetrically arranged within the larger square. Compo nents of the outputs of microphones v,F, Lv andfl-N are supplied to a mixer-175, the output of which isfedto a phase shifter and attenuator 176-which in turnjs connected'to amixer 177. I V V I The outputs of nnfcrophones; G; M ;and.( are supplied to a mixer 17 8'which is connected toia phase shifter 179 supplyingenergy-to a mixer 181. Qnt ut igqm the microphones H, N and L are connected to .a mixer 182 which supplies energy to a phase shifter 183 ,which.

' put; terminals 188, the other output;"terminal 189'being connectedtoground. g g illustration of the circuitiarrangement employed n F1gure;;5;.1szshownii ;Figure:6. A 'Ihermicrophofle fact;

ciatedcircuits comprise the mixer 177.

estates Pier the microphone F is connectedto a transformer- 191 having its secondary winding connected to the grid bf a vacuum tube 192.:"Ihecathode of the vacuum- 192 is connected to, a bias resistor 193 which is bypassedby acapacitor194t The anodes of .the vacuum tubes 192, 1961 and 201 are connected together and receive anode potential through [a common resistor 204. These anodes are also connected to a coupling capacitor 205 which is connected to one terminal ofa resistor 206having its other terminal connected to cathode biassing resistors 207 and 208fat a vacuum tube 209. 'The grid of the vacuum tube 209 is connected .to an adjustable contact 211 of the resistor 206. Suitable anode potential is. supplied to the vacuum tube 209 through an anode coupling resistor 212.}The anode of thevacuum tube 209 is connected to a capacitor 213 which is connected to the adjustable contact 214 of a resistor 215 having one end connected directly to. the cathode of'the vacuum tube 209. The adjustable contact 214 of; the resistor 215 temcomprising; a plurality of spaced pressure micro phones symmetrically arranged along a plurality of intersecting axes, means fol-variably shifting the phase and difiFerent-ially combining the outputs of said microphones to produce 'a highly, directional polar responsepattern in any desired direction.

-2. A higher order pressure gradient microphone system comprising a plurality of spaced pressure microphones'syrnmetrically arranged along a plurality of intersecting axes having equal angles therebe'tween, means for variably shifting the phase and difierentiallycomis connected to a capacitor 216 which is connected to the grid of a vacuum. tube 217.. g The grid of thevacuum tube 217 is connected to a grid resistor 218 havingone endconnected to ground. The cathode of the vacuum tube 217 is provided with a'grid bias resistor 219 having one end connected to ground. I I I I The several vacuum tubes 192, 196 and 201 comprise attenuator 176. The vacuum tube 217 and its assothe mixer=175 of Figure 5.. The vacuum tube 209 and its associated circuits comprise the phase shifter. and

The anodes. of

the. vacuum tubes in the various mixers 17 7, 181, 184, 1

and 187 are all connected together as indicated in Figure spectively, are actuated by the control 190. I

. In view oftheexplanation given in respect to'the preceding figures, it is believed that no lengthy detailed explanation of-the operation of Figures 5 and 6 is required. It was noted that the outputs of two microphone's could be combined to produce a response chara'cteristic similar to that shown in Figure 8 dependent upon whattype of microphones were employed. From the, preceding circuit arrangements, it further became apparent that such combination of voltages resulting in responses similar to that shown in Figure 8 could be combined with a voltage component of another microphone to produce the unidirectional response shown in Figure 9. .By proper selection of the magnitude of the voltage components from the several microphones, the proper resultant voltage will be derived from mixing components from each of the groups of microphones, as for example the microphones F, L and N. The introduction of attenuation and phase shift and the subsequent mixing of the resultant voltage components by thernixers 177, 181, 184 and 187 accordingly will produce a higher. order gradient response than was heretofore possible by the circuits of Figures 1 and 3. By proper design, the control 190 will operate to produce the desired highly directional unidirectional response characteristic which can be orientated along any angle or which may be moved in a scanning fashion throughout 360.

While for the purpose of illustrating and describing the present invention several particular embodiments have ,been shown and described in the drawings, it is to befunderstood that the invention is not to be limited thereto since such other embodiments are contemplated as may laccommensurate: with the spirit and scope of the invention set forth in the accompanying claims. ,Iclaimasmyinvention:. Y r u A. highenorder' pressure-gradient microphone sysbining' the outputsof said microphones to produce a highly directional polar response pattern, and means'for controlling simultaneously all said phase shifting means to rotate said polar response pattern.

3. A higher order pressure gradient microphone system comprising a plurality of spacedpre'ssure microphones symmetrically. arranged alonga plurality of intersecting axes having equal angles therebetween, means for difierentially combining the outputs of a plurality of microphones along .eachaxis, means for simultaneously variably shifting the phase of said combined out-' puts, and means for differentially combining said phase shifted outputs to produce a highly. directional polar response pattern.

4. A higher order pressuregra'dient microphonesysmicrophonesalong each axis, means for variably shifting the phase of said combined outputs, and means for differentially combining said phase shifted outputs to pro duce ahighly directional polar response pattern, and

, means for controlling simultaneously all said phase shift-' ing means to adjust said directional polar response pattern to selected orientation. i

5; A higher order pressure gradient microphone sysb. tem comprising a plurality of spaced pressure microphones arranged ina pattern having at least two dimensions, a plurality of phase shifted networks for selectively shifting the phase of the outputs of said microphones, means for differentially combining said phase shifting outputs, and means for adjusting simultaneously all of said phase shifting networks to produce a highly directional polar response pattern of selected orientation.

6. A higher order pressure gradient microphone system comprising a plurality of spaced pressure microphones arranged in a pattern having at least two dimensions, a plurality of phase shifting networks for selectively shifting the phase of the outputs of said microphones, means for difierentially combining said phase shifted outputs, and means for continuously adjusting all of said phase shifting networks to produce a rotating highly directional polar response pattern.

7. A higher order pressure gradient microphone system comprising a plurality of spaced pressure microphones symmetrically arranged along a plurality of intersecting axes, one of said microphones being at said (References 011 following page) References Cited in the file of this patent UNITED STATES PATENTS Craft et a1. June 2, 1925 Lamson Mar. 14, 1933 5 Rudolph Oct. 23, 1934 Fritz May 30, 1939 Anderson Sept. 19, 1939 10 Feldman June 17, 1941 Olson Nov. 10, 1942 Villem Mar. 14, 1944 Goodale July 16, 1946 Hays Oct. 1, 1946 Schuck Oct. 3, 1950 Kreer -Q. Apr. 10, 1951 UNITED STATES PATENT OFFICE CERTIFICATE OF CO RECTIQN Patent No.,- 2,896,189

Alpha Mo Wiggins rtif-ied that error appears in the printed specification d patent requiring correction and that the said. Letters corrected below.

It is hereby cc of the above numbere Patent should read as d m1 contact column 4, li .e 5;,

1.06 line 13, for "tube 107" read capacitor for "contacts" rea Column 3, line 15,

nmneral "196" read after "capacitor" for the 106" read m tube 107 line 14, for "capacitor "construction" read constructed o 106 line Bl, for

Signed and sealed this lst, day of March 196G,

(SEAL) Attest:

KARL "@AXLINE ROBERT c. WATSON Commissioner of Patents Attesting Oificer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent Noo 2,896,189 July 1, 1959 Alpha Ma Wiggins I It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 15, for "contacts" read contact =31 column 4, line 2, after "capacitor" for the numeral "1%" read 106 3 line 13, for "tube 106" read tube 107 line 14, for "capacitor 107" read capacitor 106 line 31, for "construction," read constructed Signed and sealed this 1st day; .of March 1960 (SEAL) Attest:

KARL AXLINE ROBERT c. WATscN Attesting Officcr Commissioner of Patents 

